The original version of Top Secret was designed by Merle M. Rasmussen,[2] and allows players and gamemasters to build their own espionage story settings. The original boxed set of the game included a 64-page rule book and a sample adventure, "Operation: Sprechenhaltestelle". The TSR Product Code for the original boxed set is TSR-7006.[3] The game was developed over a period of two years by Rasmussen and TSR editor Allen Hammack.[2] As part of the playtesting for the game, a note written on TSR stationery about a fictitious assassination plot brought the FBI to the offices of TSR Hobbies.[1]

The Top Secret game is based exclusively on 10-sided dice. All character attributes and other statistics are percentiles; some scores are rolled, and some are derived from combinations of two or more other scores. Top Secret also features Areas of Knowledge, which function similarly to skills in more modern RPGs. Characters gain experience points and progress upward in level. The levels had relatively limited in-game effects (most significantly, gained experience points were divided by the character's level but the base mission pay was multiplied by the character's level).

Top Secret characters are employed in specific bureaus—Assassination (Killing), Confiscation (Theft), or Investigation (Research)—all in the structure of an unspecified espionage agency. Despite a character's primary vocation, he may be called on to perform any type of mission. The in-game effect of a character's bureau was a 100-point experience bonus for mission objectives which fall within that bureau as well as bonus mission pay for those actions specific to the chosen bureau. An appendix in the rule book lists dozens of historical and fictional espionage organizations which could serve as employers or adversaries for missions.[2]

Original edition logo

An expansion to the game, The Top Secret Companion introduced enhancements to many game components. It included additional character classes and missions, as well as new Areas of Knowledge and abilities. A revised combat system was introduced that sped up and provided more variety to combat results. New equipment and weapons were introduced as well.[4]

Administrator's Screen and Mini-Module. Corey Koebernick (1982). (Includes Operation: Executive One) ISBN0-935696-79-2 (The agents must rescue the president, who is being held by a band of Canadian mercenaries in a haunted mansion).

TS001 - Operation: Sprechenhaltestelle. Merle Rasmussen (1980). ISBN0-935696-17-2 (German for "The place where speaking stops", this module details a town on the border between East and West [the exact location is never specified] where secrets and subterfuge are everywhere).

TS003 - Lady In Distress. Mike Carr (1982). (This module's plot involved agents parasailing to rescue a hijacked cruise ship. The module's ship plans were based on the MS Achille Lauro, which was seized by PLO terrorists in 1985 and resulted in the murder of one passenger.)

In 1987, TSR published Top Secret/S.I. ("Special Intelligence"), a revised edition designed by Douglas Niles. The TSR Product Code for the revised boxed set is TSR-7620.[5] S.I. introduced a more structured gaming environment in which players worked as agents for secret intelligence agency ORION against its evil adversary, WEB. Later source books in the product line introduce both supernatural (Agent 13) and futuristic (F.R.E.E.Lancers) adventure settings. These settings introduced several recurring characters such as Sebastian Cord and Agent 13.

Top Secret/S.I. uses a fast, simple combat system based on percentages. With as little as a single die roll, a player can know not only if a character was hit, but what part of the body was hit and the extent of damage.

Based on a character's stats, skills, bonuses and penalties, the gamemaster (Administrator) gives that character a certain percentage chance of hitting a given target. The player then rolls percentile dice; a result that is equal to or lower than the to-hit percentage succeeds. The hit location is determined by the 'ones' digit of the same roll, and hand-to-hand combat damage is determined by the 'tens' digit. Weapon damage ignores the 'tens' of the first roll, and requires a second roll based on the weapon's characteristics.

Character sheets in Top Secret/S.I. resemble agent dossiers, and are intended to provide quick and easy reference to all a player's stats and skills. They also provide a detailed map of the ten possible hit spots of a character's body, and a blank portrait area for drawing or attaching a depiction of the character.

Foul Play at Fool's Summit. Troy Denning (1989). ISBN0-88038-621-5 (Note: though this module has an ISBN, it was never actually released, as the Catacombs gamebook line was cancelled before its release.)

TSR published eight issues of 13: Assassin comic that featured stories set in the Agent 13 campaign setting bringing the story to a more modern era (1990's). The first six issues had a back-up story set in the Top Secret/S.I. setting (ORION vs. WEB) which seemed to take place at the end of the agency's covert war. Each issue also contained a miniature game and some issues included character stats for the role-playing game.

Warhawks was a four issue comic/module series that took the Top Secret/S.I. game to a time traveling setting where characters derive powers from tattoos. The four issues featured character stats and served as a campaign book in addition to the comic book adventures.

In June 2017, Merle Rasmussen announced the release of a reboot entitled "Top Secret: New World Order," a completely new iteration in the series. He had been running the game at conventions and events for two years prior to the release, adjusting the rules and user experience in real-time. The game has updated characteristics to appeal to more modern role-playing gamers, but is still a sandbox-style RPG.[6]

The Kickstarter page for Top Secret: New World Order went live on June 27, 2017.[7] The game began shipping to backers in March 2018.[8]

Jerry Epperson reviewed Top Secret in The Space Gamer No. 29.[9] Epperson commented that "I liked the game, despite its faults. The system is new enough that the situations will not become blase (as with other role-playing games) for months or years. And it would be a sound investment for any fans of the James Bond, Executioner, or Avenger stories. Others would be wise to stick with fantasy, if they cannot associate with the heroes of the present."[9]

Top Secret/SSI was ranked 38th in the 1996 reader poll of Arcane magazine to determine the 50 most popular roleplaying games of all time. The UK magazine's editor Paul Pettengale commented: "Top Secret is inspired more by The Man From U.N.C.L.E. and the lighter James Bond movies than real life. Players belong to an organisation of 'good guys' pitted against the 'bad guys' - a thinly veiled analogy of the Eastern Bloc. Gadgets and manners are more important than combat skills, and there are rarely nasty deaths."[10]